Method for coincident alignment of a laser beam and a charged particle beam

ABSTRACT

A method and apparatus for aligning a laser beam coincident with a charged particle beam. The invention described provides a method for aligning the laser beam through the center of an objective lens and ultimately targeting the eucentric point of a multi-beam system. The apparatus takes advantage of components of the laser beam alignment system being positioned within and outside of the vacuum chamber of the charged particle system.

This application is a Continuation of U.S. patent application Ser. No.14/303,227, filed Jun. 12, 2014, which application is a Continuation ofU.S. patent application Ser. No. 13/607,329, filed Sep. 7, 2012, andissued as U.S. Pat. No. 8,766,213. Both prior applications are herebyincorporated by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to charged particle beam systems, morespecifically to a system and method for laser beam alignment withincharged particle beam systems.

BACKGROUND OF THE INVENTION

Charged particle beam systems are used in a variety of applications,including the manufacturing, repair, and inspection of miniaturedevices, such as integrated circuits, magnetic recording heads, andphotolithography masks. Charged particle beams include ion beams andelectron beams.

Ions in a focused beam typically have sufficient momentum tomicromachine by physically ejecting material from a surface. Becauseelectrons are much lighter than ions, electron beams are typicallylimited to removing material by inducing a chemical reaction between anetchant vapor and the substrate. Both ion beams and electron beams canbe used to image a surface at a greater magnification and higherresolution than can be achieved by the best optical microscopes.

Since ion beams tend to damage sample surfaces even when used to image,ion beam columns are often combined with electron beam columns in dualbeam systems. Such systems often include a scanning electron microscope(SEM) that can provide a high-resolution image with minimal damage tothe target, and an ion beam system, such as a focused or shaped beamsystem, that can be used to alter workpieces and to form images. Dualbeam systems including a liquid metal focused ion beam and an electronbeam are well known.

Focused ion beam milling in many instances are unacceptably slow forsome micromachining applications. Other techniques, such as milling witha femtosecond laser can be used for faster material removal but theresolution of these techniques is lower than a typical LMIS FIB system.Lasers are typically capable of supplying energy to a substrate at amuch higher rate than charged particle beams, and so lasers typicallyhave much higher material removal rates (typically up to 7×10⁶ μm³/s fora 1 kHz laser pulse repetition rate) than charged particle beams(typically 0.1 to 3.0 μm³/s for a Gallium FIB). Laser systems useseveral different mechanisms for micromachining, including laserablation, in which energy supplied rapidly to a small volume causesatoms to be explosively expelled from the substrate. All such methodsfor rapid removal of material from a substrate using a laser beam willbe collectively referred to herein as laser beam milling.

The combination of a charged particle beam system with a laser beamsystem can demonstrate the advantages of both. For example, combining ahigh resolution LMIS FIB with a femtosecond laser allows the laser beamto be used for rapid material removal and the ion beam to be used forhigh precision micromachining in order to provide an extended range ofmilling applications within the same system. The combination of anelectron beam system, either alone or in conjunction with a FIB, allowsfor nondestructive imaging of a sample.

FIG. 1 shows a prior art dual beam system 100 having a combinationcharged particle beam column 101 and laser 104. Such a dual beam systemis described in U.S. Pat. App. No. 2011/0248164 by Marcus Straw et al.,for “Combination Laser and Charged Particle Beam System,” which isassigned to the assignee of the present application, and which is herebyincorporated by reference. U.S. Pat. App. No. 2011/0248164 is notadmitted to be prior art by its inclusion in this Background section. Asshown in the schematic drawing of FIG. 1, the laser beam 102 from laser104 is focused by lens 106 located inside the vacuum chamber 108 into aconverging laser beam 120. The laser beam 102 enters the chamber througha window 110. A single lens 106 or group of lenses (not shown) locatedadjacent to the charged particle beam 112 is used to focus the laserbeam 120 such that it is either coincident and confocal with, oradjacent to, the charged particle beam 112 (produced by charged particlebeam focusing column 101) as it impacts the sample 114 at location 116.

Integrating a laser beam system with a charged particle beam systemprovides significant challenges. Problems may arise in spatiallystabilizing the laser beam that is used in conjunction with a chargedparticle beam. The stability of the laser is determined by its abilityto precisely maintain its direction as well as its initial position withthe output aperture. The laser beam position may drift, however, overtime with variations in temperature, mechanical vibrations inside thelaser, and other environmental conditions. Periodic re-alignment of thelaser beam is therefore required to compensate for the drift. Aligning alaser beam within a charged particle beam system is currently a verytedious and time consuming manual process and requires significantexpertise. Automated beam positioning in laser beam systems is wellknown. See “Automatic beam alignment system for a pulsed infraredlaser”, Review of Scientific Instruments 80, 013102 (2009). Past systemsusually use a controller that receives signals from beam positiondetectors, and consequently issue commands for motorized opticalelements (e.g., adjustable mirrors) in order to maintain properalignment of the beam.

Unfortunately, other than aligning the laser beam manually, there iscurrently no practical system that allows for the convenient alignmentof the laser beam positioning in charge particle beam systems. The smallsample chamber of a charged particle beam system makes it difficult tohouse components needed for beam alignment systems. What is needed is amethod and apparatus for a convenient way to align a laser beam within acharged particle beam system without the need for performing thealignment manually.

SUMMARY OF THE INVENTION

An object of the invention is to provide a method and apparatus toperform an alignment of a laser beam within a charged particle beamsystem that is done in conjunction with an electron beam or focused ionbeam that provides coincident alignment with the system's eucentricpoint. According to a preferred embodiment of the present invention, abeam positioning system may be used to provide this type of alignment.

Another object of the invention is to provide a system having a vacuumchamber, a workpiece support within the vacuum chamber, a chargedparticle beam system for generating a beam of charged particles, a laserbeam system for generating a laser beam, and a laser beam alignmentsystem for aligning the laser beam, wherein the laser beam alignmentsystem has a laser beam position detector in the vacuum chamber. Thesystem will have a second beam position detector outside the vacuumchamber and beam steering mirrors to make adjustments to the laser beamso that the laser beam is aligned to the eucentric point of a chargedparticle beam system.

Another object of the invention is to provide a method of makingadjustments to a laser beam comprising a charged particle beam sourcecapable of generating a charged particle beam, providing a vacuumchamber, providing a laser beam source capable of generating a laserbeam, providing a laser beam alignment system that allows the laser beamsource to be aligned to the eucentric point of a charged particle beamsystem.

Another object of the invention is to provide a method of using a lasersystem with a charge particle beam system, wherein the steps includegenerating a charged particle beam to be used on a workpiece, generatinga laser beam to be used on the workpiece, wherein the laser beam isaligned eucentrically to the workpiece. The aligning process of thelaser beam is performed using an alignment detector that is locatedwithin the vacuum chamber of the system, as well as an alignmentdetector that is located outside the detector.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter. It should be appreciated by those skilled in the art thatthe conception and specific embodiments disclosed may be readilyutilized as a basis for modifying or designing other structures forcarrying out the same purposes of the present invention. It should alsobe realized by those skilled in the art that such equivalentconstructions do not depart from the spirit and scope of the inventionas set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more thorough understanding of the present invention, andadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a schematic view of a prior art dual-beam system includingcharged particle beam and laser beam sub-systems.

FIG. 2 shows a schematic view of an embodiment of the invention showinga laser beam alignment system.

FIG. 3 shows a schematic view of an embodiment of the invention showinga laser beam alignment system integrated with a multi-beam system.

FIG. 4 is a flowchart showing the steps of a laser beam alignmentprocess.

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The incorporation of a laser beam system with a charged particle systeminvolves difficulties with the amount of time and expertise required toalign the laser beam. The common methods for aligning a laser beaminside a vacuum chamber are very tedious and time consuming manualprocesses. Embodiments of the present invention provide advantages overcommon methods of manually aligning a laser beam within a chargedparticle beam system. Some embodiments of the present invention providea system for the alignment of a laser beam within a charged particlebeam system using laser position sensors.

FIG. 2 shows a schematic view of a laser beam alignment system 201according to a preferred embodiment that is used in charged particlebeam system. A laser beam source 205 generates a laser beam 204. Twofast steering mirrors 202, 203 are positioned to control the directionof the laser beam 204. Fast steering mirrors (FSM) have the ability tomechanically tilt the mirror in order to control the direction of thelaser beam. FSMs are well known to those having skill in the art, andneed not be described further herein. Other types of beam steeringmirrors are well known in the art, including scanning mirrors. Agalvanometer based scanning mirror can be used in place of FSMs and arealso well known to those having skill in the art. Fast steering beammirrors 202 and 203 are connected by lines 207 and 208 to fast steeringmirror controllers 206 and 213. Voice coils, or devices that aregalvanometers or act like galvanometers, are used in fast steeringmirrors to use the electrical signals it receives from the controllers.Fast steering mirror controllers 206 and 213 control the fine pointingand tracking of the laser beams.

Fast steering mirror 202 is coupled to the quad cell detector 210 viathe controller 206. Quad cell detector 210 is located outside thechamber wall 209 of the charged particle beam system 201. Chamber wall209 separates the vacuum chamber of the charged particle beam system 201from the outside. As laser beam 204 reflects off of fast steering mirror202 and 203, laser beam 204 is split with a beam sampler, or beamsplitter 211, to form a second beam 223. Beam splitter 211 is aconventional beam splitter that separates the beam into two componentbeams. The power splitting between the two component beams is determinedby the reflection and transmission coefficients of the beam splitter.Second beam 223 is directed to quad cell detector 210. Generally, secondbeam 223 is the weaker beam of the two split beams. Quad cell detector210 and quad cell detector 215 can be conventional alignment detectorsthat are capable of detecting the alignment, or the position, of a laserbeam source. A position sensitive detector (PSD) is another type of analignment detector. A PSD can be generally a photoelectric device thatconverts an incident light, or laser beam, into continuous positiondata. In other words, a PSD can detect and record the position ofincident light beams. A PSD can have various configurations, including aquadrant detector configuration or a dual axis lateral effect detectors.The purpose of these two types is to sense the position of the beamcentroid in the X-Y plane orthogonal to the optical axis. In order tomeasure the X and Y position from the PSD, four electrodes are attached(not shown) to the detector and an algorithm then processes the fourcurrents generated by photoabsorption. Quad cell detector 210 isgenerally fixed and provides the positional data of laser beam 204 toFSM controller 206. It then makes the adjustments in the fast steeringmirror 202 so that the laser beam comes to an alignment point 220. Laserbeam 204 enters the vacuum chamber via window 212 where the laser beamis focused using objective lens 214.

Quad cell detector 215 is coupled to controller 213 and fast steeringmirror 203. Quad cell detector 215 is located inside the chamber wall209 within the vacuum chamber. Quad cell detector 215 works with thefast steering mirror controller 213 and fast steering mirror 203 tomechanically align the laser beam 204 to an alignment point 221. Thein-chamber quad cell detector 215 is able to be positioned remotely withrelatively good positional accuracy and high repeatability. Other typesof alignment detectors can perform the detection of the laser alignmentor position detection. A quad cell detector is generally a uniform diskwith two gaps across its surface. It generates four signals from eachquadrant of the disk. The laser beam is varied on the disk until thesignal strength of each quadrant of the disk is equal. The in-chamberquad cell detector 215 is capable of being retracted or moved to clearthe path for laser beam 204 with retractor 222. Retractor 222 can becontrolled remotely from outside the vacuum chamber 360 and can be anymechanism that can move the quad cell detector 215 from its alignmentposition to a position away from laser beam pathway. The mechanism canbe a lever that is manually adjusted in the X-Y-Z direction, or themechanism can be an electronic component that can electronically adjustthe quad cell detector 215 in the X-Y-Z direction. The mechanism mustallow the retractor 222 to move the quad cell detector 215 in and out ofthe proper position accurately and repeatedly. The retractor 222 isaligned to the optical axis of the objective lens 214. In one embodimentof the invention, the objective lens 214 provides a hard stop for thequad cell detector 215 (not shown). It would include an electronicallycontrolled actuator arm that slides the quad cell detector 215 in andout of the proper aligned position.

FIG. 3 shows a system 300 according to a preferred embodiment of thepresent invention that combines a focused laser beam 216 (produced by alaser 306) for rapid material removal with a focused ion beam (FIB) 352(produced by a FIB column 304) for further material processing and anelectron beam 350 (produced by a SEM column 302) for monitoring thematerial removal process. A laser 306 directs a laser beam 308 towards afirst steering mirror 202, which reflects the laser beam 308 to form afirst reflected beam 312. First reflected beam 312 is directed towards asecond steering mirror 203, which reflects the first reflected beam 312to form a second reflected beam 322 which is directed throughtransparent window 212 in vacuum chamber 360. By “transparent” it ismeant that the window is transparent to wavelengths of the particulartype of laser being used. Steering mirrors 202 and 203 (or a similarreflecting elements) are used to adjust the position of the laser beam216 on the sample 320.

An objective lens 214 focuses the laser beam 322 (which may besubstantially parallel) into a focused laser beam 216 with a focal pointat or near to the surface of a sample 320. In some embodiments, laserbeam 216 is preferably capable of being operated at a fluence greaterthan the ablation threshold of the material in sample 320 beingmachined. Preferred embodiments of the invention could use any type oflaser, now existing or to be developed, that supplies sufficientfluence. A preferred laser provides a short, nanosecond to femtosecond,pulsed laser beam. Suitable lasers include, for example, a Ti:Sapphireoscillator or amplifier, a fiber-based laser, or an ytterbium- orchromium-doped thin disk laser. Other embodiments may use a laser havingless fluence that reacts with the workpiece without ablation, such asthermally induced chemical desorption processes using a laser or theprocess of laser photochemistry. The current system allows for themanipulation of the fast steering mirrors 202 and 203 to be preciselycontrolled with the adjustments calculated by the reading of the quadcell detectors 210 and 215 so that the alignment of the laser beam canbe made through the center of the objective lens 214 and ultimately,targeting the eucentric point of the target 320. Quad cell detector 214is located as close to the output of the objective lens 214 aspractically possible to provide better precision of the laser beam andto prevent damage to the detector induced by the focused laser beam.

Sample 320 is typically positioned on a precision stage (not shown),which preferably can translate the sample in the X-Y plane, and morepreferably can also translate the work piece in the Z-axis, as well asbeing able to tilt and rotate the sample for maximum flexibility infabricating three-dimensional structures. System 300 optionally includesone or more charged particle beam columns, such as an electron beamcolumn 302, an ion beam column 304, or both, which can be used forimaging the sample to monitor the laser ablation process, or for otherprocessing (such as FIB-milling) or imaging tasks. Ion beam column 304typically forms a beam of ions 352 which may be focused onto the samplesurface 320 at or near the focal point of the laser beam 318. FIB column304 may also be capable of scanning ion beam 352 on the substratesurface to perform imaging and/or FIB milling. System 300 may alsoinclude a gas injection 330 system for supplying a precursor gas thatreacts with the substrate 320 in the presence of the electron beam 350or focused ion beam 352.

As is well-known in the prior art, the electron beam column 302comprises an electron source (not shown) for producing electrons andelectron-optical lenses (not shown) for forming a finely focused beam ofelectrons 350 which may be used for SEM imaging of the sample surface320. The beam of electrons 350 can be positioned on, and can be scannedover, the surface of the sample 320 by means of a deflection coil orplates (not shown). Operation of the lenses and deflection coils iscontrolled by power supply and control unit (not shown). It is notedthat the lenses and deflection unit may manipulate the electron beamthrough the use of electric fields, magnetic fields, or a combinationthereof.

Sample chamber 360 preferably includes one or more gas outlets forevacuating the sample chamber using a high vacuum and mechanical pumpingsystem under the control of a vacuum controller (not shown). Samplechamber 360 also preferably includes one or more gas inlets throughwhich gas can be introduced to the chamber at a desired pressure.

FIG. 4 is a flowchart showing the steps of an algorithm for thealignment of the laser beam system 300 of FIG. 3 in accordance with oneof the embodiments. Before the algorithm is begun, in step 401, the beammust be coarsely focused and aligned so that the laser beam is alignedto point 220. This step should be done with the system vented and theisolation table, if any, floated. Laser beam 204 is further positionedso that it passes through the laser injection port (LIP) window 214 andinto the vacuum chamber 360. Adequate coarse focus will generally resultin the formation of visible plasma when the vacuum chamber is open. Theoptical emission from the plasma will enable the user to roughlyposition the focus of the laser beam close to the eucentric point of thecolumn (the LIP window 214 is capable of being manually translated in X,Y, and Z from outside the chamber). The LIP window 214 can be shifted inthe X and Y directions, which positions the beam on the sample. The LIPwindow 214 can be moved in and out in the Z axis so that that focus ofthe beam can be directed to a desired location, e.g., so that the beamis aligned with the eucentric point of the system. After the manualcoarse focus and positioning of the beam, the system 300 is pumped downand the electron beam turned on. Generally, the manual manipulation forcoarse focusing will only need to be done the first time the laser isaligned with system 300.

In step 402, quad cell 215 is moved to its pre-aligned position in thelaser beam pathway. In step 403, the position of the laser beam 204 onthe beam splitter 211 is monitored at quad cell detector 210. Beamposition information from quad cell detector 210 is converted to ausable signal (via the fast steering mirror 202 and controller 206). Insteps 404 and 411, controller 206 works with the voice coils of faststeering mirror 202, which provides the precision adjustments needed tosteer the beam to be coincident with point 220. Steps 404 and 411 areperformed repeatedly until the beam is aligned properly to point 220.

Once the beam is aligned properly to point 220, in step 405, theposition of the beam at the objective lens 214 is monitored by quad celldetector 215. As with quad cell detector 210, beam position informationfrom quad cell detector 215 is converted to a voltage (via the faststeering mirror 203 and controller 213) that is applied to the voicecoils of fast steering mirror 203. The adjustments made to fast steeringmirror 203 with controller 213 is repeatedly, sequentially, anditeratively made until the beam is coincident with point 221 in step407. If the beam is targeted properly on point 221, in step 408, thebeam position is once again monitored at beam splitter 211 with quadcell detector 210. In step 409, the beam is monitored to be targeted onpoint 220. The whole process is repeated until the beam is aligned withboth points 220 and 221.

Once alignment of beam is made to be coincident with points 220 and 221,the beam enters LIP window 212. The location of the beam is checked onfast steering mirror 203. It is necessary to use fast steering mirror203 to direct the beam so that it is centered on sample 320 because thefast steering mirror 203 is used to scan the beam on sample 320. If thebeam is not centered on the fast steering mirror 203, the scan may notbe linear across the scan field. Not having it centered may also limitthe extent of the scan in one direction. In cases where fast steeringmirror 203 is not centered on sample 320, the entire mirror assembly ismoved in the X/Y directions in step 410 as needed to center the beam. Inthis process, the angle of the mirror is generally not changed.

Once the laser beam is aligned to be coincident with the system'seucentric point, a retractor 222 is used to move quad cell detector 215out of the beam path to allow the beam to be incident with the sample.In use, the laser beam is focused to the eucentric point of the chargedparticle system. The eucentric point is typically a prior known distancefrom the end of the electron column 302. The focus of electron beam 350is adjusted such that the focus distance is the same as the eucentricpoint of the system and the workpiece height is adjusted until thesample comes into focus. A laser spot is then machined on the sample andcompared to the system's eucentric point. If the laser spot is notpositioned at the eucentric point, the LIP window 212 is manuallyadjusted until the correct position is achieved. The alignment proceduredetailed above is repeated and the manual positioning of the laser spotis performed again. The whole process is iterated until the beam isaligned and positioned at the eucentric point and the electron beam 350is aligned to the eucentric point. Once the alignment is set, LIP window212 position is fixed.

The invention described above has broad applicability and can providemany benefits as described and shown in the examples above. Theembodiments will vary greatly depending upon the specific application,and not every embodiment will provide all of the benefits and meet allof the objectives that are achievable by the invention. For example, ina preferred embodiment TEM samples are created using a gallium liquidmetal ion source to produce a beam of gallium ions focused to asub-micrometer spot. Such focused ion beam systems are commerciallyavailable, for example, from FEI Company, the assignee of the presentapplication. However, even though much of the previous description isdirected toward the use of FIB milling, the milling beam used to processthe desired TEM samples could comprise, for example, an electron beam, alaser beam, or a focused or shaped ion beam, for example, from a liquidmetal ion source or a plasma ion source, or any other charged particlebeam. Further, although much of the previous description is directed atsemiconductor wafers, the invention could be applied to any suitablesubstrate or surface.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made to the embodiments described herein withoutdeparting from the spirit and scope of the invention as defined by theappended claims. Moreover, the scope of the present application is notintended to be limited to the particular embodiments of the process,machine, manufacture, composition of matter, means, methods and stepsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the disclosure of the present invention,processes, machines, manufacture, compositions of matter, means,methods, or steps, presently existing or later to be developed thatperform substantially the same function or achieve substantially thesame result as the corresponding embodiments described herein may beutilized according to the present invention. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

We claim as follows:
 1. A method for laser alignment within a chargedparticle beam system, comprising: positioning a laser beam so that itpasses through a laser injection port window and into a vacuum chambertoward a workpiece; based on information from a first alignmentdetector, adjusting the laser beam so that it is pointed on a firstdesignated point located before an objective lens and so that it passesthrough the objective lens; moving a second alignment detector to adesignated position in the laser beam pathway; monitoring the positionof the beam on the objective lens with second alignment detector; basedon information from the second alignment detectors, adjusting the laserbeam so that the laser beam is pointed to a second designated pointaligned with the workpiece and so that the laser beam is alignedeucentrically to the workpiece.
 2. The method of claim 1 furthercomprising, after adjusting the beam to the second point, based oninformation from the first alignment detector, monitoring and adjustingthe position of the laser beam again so that it is pointed to the firstpoint.
 3. The method of claim 1 wherein the process of adjusting thelaser beam on the first designated point and the second designated pointis done repeatedly until the laser beam is aligned to both the firstpoint and the second point.
 4. The method of claim 1 further comprisingmachining a spot on the workpiece with the laser and comparing to aeucentric point.
 5. The method of claim 4 wherein if the laser spot doesnot match with the eucentric point, repeating the procedure until theymatch.
 6. The method of claim 1 wherein adjusting the laser beam to beeucentrically aligned with the workpiece further includes adjusting thelaser beam to a eucentric point of a focused ion beam system directedtoward the workpiece, the method further comprising milling theworkpiece with the focused ion beam system directed toward the workpiecein the vacuum chamber.
 7. The method of claim 6 further comprisingimaging the workpiece with an electron beam system directed toward theworkpiece in the vacuum chamber to monitor the ion beam milling.
 8. Themethod of claim 1 further comprising milling the workpiece with thelaser beam.
 9. The method of claim 8 further comprising imaging theworkpiece with an electron beam system directed toward the workpiece inthe vacuum chamber to monitor the laser beam milling.
 10. A multi-beamsystem, comprising: a vacuum chamber; a workpiece support for supportinga workpiece within the vacuum chamber; a focused ion beam system forgenerating a focused ion beam, said ion beam directed toward theworkpiece and operable to remove material from the workpiece; a laserbeam system for generating a laser beam for processing the workpiece inthe vacuum chamber; an electron beam system for monitoring the materialremoval process; an objective lens; a laser beam alignment systemoperable to adjust the position laser beam through the center of theobjective lens and direct it to a eucentric point of the workpiece. 11.The multi-beam system of claim 10 in which the laser beam is operable ata fluence greater than an ablation threshold of the workpiece.
 12. Themulti-beam system of claim 11 in which the laser beam is a nanosecond tofemtosecond pulsed laser beam.
 13. The multi-beam system of claim 10 inwhich the laser beam operable at a fluence that reacts with theworkpiece without ablation.
 14. The multi-beam system of claim 10 inwhich the laser beam is operable to cause thermally induced chemicaldesorption at the workpiece.
 15. The multi-beam system of claim 10 inwhich the laser beam is operable to cause laser photochemistry reactionsat the workpiece.
 16. The multi-beam system of claim 10, wherein thelaser beam alignment system includes first and second alignmentdetectors, and is operable to, based on information from a firstalignment detector, adjust the laser beam so that it is pointed on afirst designated point located before the objective lens and so that itpasses through the objective lens; the laser beam alignment systemfurther operable to monitor the position of the beam on the objectivelens with second alignment detector and, based on information from thesecond alignment detectors, adjust the laser beam so that the laser beamis pointed to a second designated point aligned with the workpiece andso that the laser beam is aligned eucentrically to the workpiece. 17.The multi-beam system of claim 16 in which the laser beam alignmentsystem is further operable to, after adjusting the beam to the secondpoint, based on information from the first alignment detector, monitorand adjust the position of the laser beam again so that it is pointed tosaid first point.
 18. The multi-beam system of claim 16 in which thesecond alignment detector is a quad cell detector.
 19. The multi-beamsystem of claim 16 wherein the second alignment detector is locatedclose enough to the output of the objective lens to precisely measurethe laser beam location on the objective lens and to prevent damage tothe second alignment detector induced by the focused laser beam.